linux-kernel - RE: [PATCH v12 11/20] cxl/pci: Add RCH downstream port AER register discovery

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Date:   Fri, 27 Oct 2023 15:12:47 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Robert Richter <rrichter@....com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
CC:     <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Terry Bowman <terry.bowman@....com>,
        Robert Richter <rrichter@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: RE: [PATCH v12 11/20] cxl/pci: Add RCH downstream port AER register
 discovery

Robert Richter wrote:
> From: Terry Bowman <terry.bowman@....com>
> 
> Restricted CXL host (RCH) downstream port AER information is not currently
> logged while in the error state. One problem preventing the error logging
> is the AER and RAS registers are not accessible. The CXL driver requires
> changes to find RCH downstream port AER and RAS registers for purpose of
> error logging.
> 
> RCH downstream ports are not enumerated during a PCI bus scan and are
> instead discovered using system firmware, ACPI in this case.[1] The
> downstream port is implemented as a Root Complex Register Block (RCRB).
> The RCRB is a 4k memory block containing PCIe registers based on the PCIe
> root port.[2] The RCRB includes AER extended capability registers used for
> reporting errors. Note, the RCH's AER Capability is located in the RCRB
> memory space instead of PCI configuration space, thus its register access
> is different. Existing kernel PCIe AER functions can not be used to manage
> the downstream port AER capabilities and RAS registers because the port was
> not enumerated during PCI scan and the registers are not PCI config
> accessible.
> 
> Discover RCH downstream port AER extended capability registers. Use MMIO
> accesses to search for extended AER capability in RCRB register space.
> 
> [1] CXL 3.0 Spec, 9.11.2 - System Firmware View of CXL 1.1 Hierarchy
> [2] CXL 3.0 Spec, 8.2.1.1 - RCH Downstream Port RCRB
> 
> Co-developed-by: Robert Richter <rrichter@....com>
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> ---
>  drivers/cxl/core/core.h |  1 +
>  drivers/cxl/core/pci.c  |  6 ++++++
>  drivers/cxl/core/regs.c | 36 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 43 insertions(+)
> 
> diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
> index 45e7e044cf4a..f470ef5c0a6a 100644
> --- a/drivers/cxl/core/core.h
> +++ b/drivers/cxl/core/core.h
> @@ -73,6 +73,7 @@ struct cxl_rcrb_info;
>  resource_size_t __rcrb_to_component(struct device *dev,
>  				    struct cxl_rcrb_info *ri,
>  				    enum cxl_rcrb which);
> +u16 cxl_rcrb_to_aer(struct device *dev, resource_size_t rcrb);
>  
>  extern struct rw_semaphore cxl_dpa_rwsem;
>  
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index 7c3fbf9815e9..cbccc222bb91 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -722,6 +722,12 @@ static bool cxl_report_and_clear(struct cxl_dev_state *cxlds)
>  
>  void cxl_setup_parent_dport(struct device *host, struct cxl_dport *dport)
>  {
> +	struct device *dport_dev = dport->dport_dev;
> +	struct pci_host_bridge *host_bridge;
> +
> +	host_bridge = to_pci_host_bridge(dport_dev);
> +	if (host_bridge->native_cxl_error)
> +		dport->rcrb.aer_cap = cxl_rcrb_to_aer(dport_dev, dport->rcrb.base);

Nothing in this function has a compile dependency on CONFIG_PCIEAER_CXL
the enumeration can be done unconditionally, it's the usage that needs
to be gated.

I believe I had commented on this before, given the late hour I will
need to fix this up post -rc1.